Funding is requested under RFA NS/AG-91-03 to study the mechanisms of neuronal cell death in normal human aging and Alzheimer's disease. The cognitive decline associated with aging and the human neurodegenerative diseases (e.g. Alzheimer's disease, Parkinson's disease and Huntington's disease) is most certainly caused by neuronal dysfunction, eventual cell death, and loss of synapses (1). But, what are the causes of neural degeneration and death? The "calcium hypothesis of brain aging" (2) proposes that changes in the cellular mechanisms that act to modulate the concentration of free intracellular calcium ([Cai]) within the neuron contribute to the causative factors leading to neuronal dysfunction and degeneration. A similar hypothesis has also been proposed to explain the neurodegenerative processes occurring in Alzheimer's disease (AD). The "calcium hypothesis of AD" proposes that a loss of Cai homeostasis is the final common pathway to neuronal degeneration. Unfortunately, very little is known about the effects of human aging and AD on neuronal Ca2+ homeostatic processes. This proposal describes a focused study of the properties of neuronal plasma membrane Na+/Ca2+ countertransport in the aging rat brain, the aging human central nervous system (CNS) and in AD. The specific aims of this study are as follows: 1. Determine the effect of an animal model of aging, normal human aging and AD on several important molecular and kinetic properties of neuronal plasma membrane Na+/Ca2+ countertransport. a. the Km and Vmax for Ca2+ activation of Ca2+ transport b. the passive permeability of the plasma membrane to Ca2+ c. evidence for the presence of K+ sensitive and insensitive forms of the Na+/Ca2+ exchanger in rat brain and the human central nervous (CNS) d. the effect of lipophilic peptides (including betaA41-40, betaA425-35, and substance P analogs) on the Na+/Ca2+ exchanger e. molecular weight determination by SDS PAGE and western blot analysis using monoclonal antibodies (MAB) raised to peptide sequences of the dog heart exchanger f. the cellular location of the exchanger depicted by immunocytochemistry using the same MAB 2. Analyze the relationship between age of onset of AD and items 1.a-e above. 3. Using tissues from well documented familial AD, determine the effect on Km and Vmax for Ca2+ activation of Ca2+ transport and western blot analysis.